Members of the hedgehog family of signaling molecules mediate many important short- and long-range patterning processes during invertebrate and vertebrate embryonic, fetal, and adult development. In Drosophila melanogaster, a single hedgehog gene regulates segmental and imaginal disc patterning. In contrast, in vertebrates, a hedgehog gene family (e.g., in mammals, SHH, DHH, IHH) is involved in the control of proliferation, differentiation, migration, and survival of cells and tissues derived from all three germ layers, including, e.g., left-right asymmetry, CNS development, somites and limb patterning, chondrogenesis, skeletogenesis and spermatogenesis.
Hedgehog signaling occurs through the Hedgehog pathway which includes interactions between hedgehog ligand with the hedgehog receptor, Patched (Ptch), and the co-receptor Smoothened (Smo). There are two mammalian homologs of Ptch, Ptch-1 and Ptch-2 (“collectively “Ptch”), both of which are 12 transmembrane proteins containing a sterol sensing domain (Motoyama et al., Nature Genetics 18: 104-106 (1998), Carpenter et al., P.N.A.S. (U.S.A.) 95: 13630-40 (1998)). The interaction of Hedgehog with Ptch triggers a signaling cascade that results in the regulation of transcription by zinc-finger transcriptions factors of the Gli family.
Malignant tumors (cancers) are the second leading cause of death in the United States, after heart disease (Boring et al., CA Cancel J. Clin. 43:7 (1993)). Cancer features can include an the increase in the number of neoplastic cells which proliferate to form a tumor mass; invasion of adjacent tissues by these neoplastic tumor cells; and generation of malignant cells which eventually spread via the blood or lymphatic system to regional lymph nodes and to distant sites. Cancer manifests itself in a wide variety of forms, characterized by different degrees of invasiveness and aggressiveness.
Reactivation of the Hedgehog pathway has been implicated in a wide variety of cancers and carcinogenesis. The earliest examples of Hedgehog signaling in cancers came from the discovery that Gorlin's syndrome, in which patients frequently suffer basal cell carcinomas and are also predisposed to medulloblastomas and rhabdomysocarcomas, is due to an inactivating mutation in Ptch, resulting in Hedgehog pathway activation (Hahn et al 1998 Cell 85:841; Johnson et al. 1996, Science 272:1668). Subsequently inactivating mutations in Ptch and/or activating mutations in Smo were found to be responsible for sporadic basal cell carcinomas (Xie et al. 1998, Nature 391: 90).
Hedgehog pathway proteins and genes have also been implicated in esophageal cancer (Ma, X., et al. Int J Cancer, 118: 139-148, 2006; Berman, D. et al. Nature, 425: 846-851, 2003) and are highly expressed in the majority of chemotherapy-resistant esophageal cancer specimens (Sims-Mourtada, J. et al. Clin Cancer Res, 12: 6565-6572, 2006). More cancers where the Hedgehog pathway are involved include biliary tract cancers (Berman, D. et al. Nature, 425: 846-851, 2003), melanoma (Stecca, B., et al. Proc Natl Acad Sci USA, 104: 5895-5900, 2007), and stomach cancer (Berman, D. et al. Nature, 425: 846-851, 2003; Ma, X., et al. Carcinogenesis, 26: 1698-1705, 2005). Tumors that contain highly proliferative “tumor stem cells” and which represent areas of therapy include glial cell cancers (Clement, V., et al. Curr Biol, 17: 165-172, 2007), prostate cancers (Li, C., Heidt, et al. Cancer Res, 67: 1030-1037, 2007), breast cancers (Liu, S., et al. Cancer Res, 66: 6063-6071, 2006), multiple myelomas (Peacock, C. D., et al. PNAS, 104: 4048-4053, 2007), and colon cancers (Ricci-Vitiani, L., et al. Nature, 445: 111-115, 2007).
In addition, the Hedgehog pathway plays a role in regulating cancer stem cells, which are discrete tumor cell populations that display highly enhanced survival, self-renewal, and tumorigenicity properties (Beachy, P. A., et al. Nature, 432: 324-331, 2004). Activation of the Hedgehog pathway has been shown to play a role in cancer stem cells of the breast (Liu, S., et al. Cancer Res, 66: 6063-6071, 2006), central nervous system (Clement, V., Curr Biol, 17: 165-172, 2007) as well as in hematological malignancies (Peacock, C. D., PNAS, 104: 4048-4053, 2007).
Modulators of the Hedgehog pathway are described herein.